"The King James translation makes a promise in 'Thou shalt,' meaning that men will surely triumph over sin. But the Hebrew word, the word timshel--'Thou mayest'--that gives a choice. It might be the most important word in the world. That says the way is open. That throws it right back on a man. For if 'Thou mayest'--it is also true that 'Thou mayest not.' Don't you see?...and there are millions more who feel predestination in 'Thou shalt.' Nothing they may do can interfere with what will be. But 'Thou mayest'! Why, that makes a man great, that gives him stature with the gods, for in his weakness and his filth and his murder of his brother he has still the great choice. He can choose his course and fight it through and win. It is easy out of laziness, out of weakness, to throw oneself into the lap of deity, saying 'I couldn't help it; the way was set.' But think of the glory of the choice! That makes a man a man...The human soul. It is a lovely and unique thing in the universe. It is always attacked and never destroyed--because 'Thou mayest.'"
This passage seems to fit perfectly with what Lewis is saying in this chapter. We know what is the right thing to do, but we don't do it most of the time. Lewis talks of the materialist view-that of everything just coming to be because of chance, or a series of chances-and the religious view-there is some sort of mind behind the universe that is conscious and has purpose-and neither of these laws can be proven correct based on science, because science only observes by experimentation and does not provide answers to questions like, "why is there a universe?" and "Why does it go on as it does?". But since we can only look in ourselves to explain this, and since we are governed by laws and therefore do not exist on our own, there has to be some "Power behind the facts, a Director, a Guide."
For some reason God has chosen humanity to bear His image and to live under this Moral law. However, we do have a choice..."Thou mayest." Why He chose us, I do not know. But I think we should bear this honor with humility and respect and be conscious of our every decision because the Creator of the ENTIRE universe has bestowed it upon us.